Description: (Applicant's Description) The IUCC Mouse Core provides services for the production of transgenic mouse lines using both blastocyst injection of embryonic stem (ES) cells and pronuclear injection of DNA. The latter method allows production of mice after targeted modification of specific DNA sequences in the mouse genome. The core will provide the following services: 1) generation of embryonic stem cell clones following introduction of targeting constructs by electroporation; 2) blastocyst injection of clones identified by the investigator using standard DNA methods as appropriately targeted; 3) embryo transfer of injected blastocysts; and 4) provision of resulting chimeric mice for further breeding and study by investigators. For pronuclear injections: 1) harvesting and injection of single cell embryos by DNA plasmids provided by the investigator; and 2) provision of resulting live pups for DNA analysis by investigators to identify transgenic animals. In either case, DNA constructs are generated by IUCC members and provided to the core and core personnel will provide advice concerning construction of plasmids, breeding, and maintenance of the transgenic colony. Overall, the core provides transgenic mice to IUCC investigators in a timely and cost-efficient manner.